Knowledge Bank

[FUGURE] The microwave spectrum of $\gamma$-valerolactone has been studied in the region 15 to 40 GHz. The spectrum is fairly dense and has been assigned to a single conformer with ground state rotational constants (in MHz): A= 5337.16, B= 2193.59, and C = 1668.04. These indicate a structure in which the ring is twisted and the methyl group is equatorial. Two series of strong vibrational satellites have also been observed, due to ring deformation modes. The barrier to rotation of the $CH3$ group has been determined from doublet splittings to be $V3=904\pm 20$ cal $mole-1$.